Cholesterol biosynthesis in chicken liver: effect of triiodothyronine.

The effect of a single injection of L-triiodothyronine (T3) on the levels of liver cholesterol and liver 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) has been studied in chicken. A minimal dose of 8 micrograms/animal produces its maximal effects after 12 h. T3 enhances both HMGR activity and cholesterol levels in liver. Both effects are suppressed when protein synthesis inhibitors (actinomycin D or cycloheximide) are administered along with the hormone. Solubilized and membrane-bound HMGR activities are equally influenced by the hormone. The in vitro addition of T3 does not affect the HMGR activity. It is concluded that T3 increases cholesterol biosynthesis in chicken liver through the activation of de novo protein synthesis.